[3.10] Remove a redundant assignment in Tools/unittestgui/unittestgui.py (GH-21438) (GH-26171)

(cherry picked from commit a42d98ed91cd1f08b2e9734ca6ca136dd10dff5d)

Co-authored-by: Serhii Hidenko <shidenko97@gmail.com>
diff --git a/Tools/unittestgui/unittestgui.py b/Tools/unittestgui/unittestgui.py
index c3b5fa4..4fc5930 100755
--- a/Tools/unittestgui/unittestgui.py
+++ b/Tools/unittestgui/unittestgui.py
@@ -54,7 +54,6 @@ class BaseGUITestRunner(object):
     def __init__(self, *args, **kwargs):
         self.currentResult = None
         self.running = 0
-        self.__rollbackImporter = None
         self.__rollbackImporter = RollbackImporter()
         self.test_suite = None